Calcium pyrophosphate dihydrate (CPPD) deposition disease is an arthropathy characterized by the accumulation of CPPD crystals in articular tissues including synovial fluid. CPPD crystals contribute significantly to the chronic pain and tissue damage of joint degeneration, and they induce neutrophil activation, fibroblast and chondrocyte mitogenesis and production of MMP and prostaglandins in vitro. CPPD deposition is associated with acute inflammatory attacks (pseudogout), chronic arthritis, and degenerative joint disease. Although only about 10% of the CPPD patient population ever experiences acute inflammatory attacks, the majority of patients with chronic arthritis of the large joints have CPPD deposition. CPPD crystals play a significant role in arthritic disease progression. The synovial fluids sampled from patients with degenerative joint disease contain CPPD crystals, cartilage fragments, and matrix metalloproteinases (MMP) such as collagenase and stromelysin. (Swan, A. B. et al. (1994) Ann. Rheum. Dis. 53:467-470; Lohmander, L. S. et al. (1993) Arthritis. Rheum. 36:181-189).
Deposition of CPPD crystals appears to be related to excess levels of extracellular calcium, pyrophosphate (PPi), or both. Whereas elevated calcium levels do not appear to be a major contributing factor to CPPD deposition in joints, elevated PPi levels have been noted in the synovial fluids from patients with CPPD deposition. Synovial fluid PPi seems to be produced by joint tissues since PPi levels are higher in the synovial fluid than in the plasma. The fact that in vitro cartilage explants release PPi into the extracellular medium also suggests that cartilage is a primary source of PPi (Ryan, L. M. et al. (1996) J. Rheumatol. 23:214-219).
Enzymes that hydrolyze nucleotide triphosphates and release PPi are called nucleotide pyrophosphohydrolases (NTPPH). NTPPH activity is found in synovial fluid and correlates with the production of PPi. Elevated ATP levels have been found in joint fluids of patients with CPPD deposition, and addition of extracellular ATP to joint tissues and fluids results in the production of PPi (Park, W. I. et al. (1996) J. Rheumatol. 23:665-671). Molecules exhibiting NTPPH activity can be extracted from cartilage using detergent, and the levels of molecules demonstrating NTPPH activity are higher in extracts from cartilage containing CPPD crystals than from cartilage lacking crystals. Matrix vesicles released from articular cartilage show high NTPPH activity and generate CPPD in vitro in the presence of calcium and ATP (Derfus, B. A. et al. (1992) Arthritis. Rheum. 35:231-240).
A protein demonstrating NTPPH and having a molecular weight of 61 kD activity was recently obtained from medium conditioned with porcine articular cartilage explant. The first 26 residues of the amino-terminal sequence were determined and showed no homology to any protein in public databases. Antipeptide antibodies were generated against the 61 kD porcine protein, and the antisera identified the original 61 kD protein and an additional 127 kD vesicle-associated protein in conditioned medium from cultures of both chondrocytes and cartilage explants. The 61 kD isoform is believed to be a catalytically active proteolytic fragment of the 127 kD protein. Both the 61 kD and the 127 kD isoforms were identified in human synovial fluids, and a 100 kD protein was identified in human serum. Using the antipeptide antibody on immunoblots of tissue extracts, NTPPH expression was found to be restricted to the articular tissues in which CPPD deposition occurs: hyaline cartilage, fibrocartilage, tendon, and ligament (Cardenal, A. et al. (1996) Arthritis Rheum. 39:252-256; Cardenal, A. et al. (1996) Arthritis Rheum. 39:245-251).
The discovery of a new human nucleotide pyrophosphohydrolase and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of arthropathies, immunological disorders, and cancers.